Methods and apparatus for selecting a base station transceiver system based on service communication type

ABSTRACT

Techniques for use in selecting a base station transceiver system for communication with a mobile station are described. The mobile station is connected to a first base station transceiver system, and scans to identify a second base station transceiver system for communication. The mobile station further identifies that the second base station transceiver system provides a predetermined communication service, and that the first base station transceiver system fails to provide the predetermined communication service. In response to identifying, the mobile station causes the second base station transceiver system to be selected for communication over the first base station transceiver system even if the signal quality of the second base station transceiver system is worse than that of the first base station transceiver system. Identifying whether the first and second base station transceiver system provide the predetermined communication service is based on parameters transmitted from the first and second base station transceiver systems.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of and claims priority to U.S.non-provisional patent application having application Ser. No.13/164,419, filed Jun. 20, 2011, which is a continuation of and claimspriority to U.S. non-provisional patent application having applicationSer. No. 10/693,346 and filing date of 24 Oct. 2003, now U.S. Pat. No.7,970,429, which are both hereby incorporated by reference herein.

BACKGROUND

1. Field of the Invention

The present invention relates generally to mobile stations and basestation transceiver systems, and more particularly to the selection ofbase station transceiver systems based on service communication type(e.g. 2G or 3G communication service).

2. Description of the Related Art

A wireless communication device, such as a cellular telephone or mobilestation, is often capable of making and receiving voice calls and/orsending and receiving data over a wireless communication network. Beforeit is able to do this, the cellular mobile station selects, acquires,and registers with one of a plurality of communication networks whichare available within a given geographic coverage area. After registeringwith the selected network, the mobile station operates in an idle modewhere it “camps-on” a particular wireless communication channel of thenetwork to monitor for its calls or messages. The mobile station alsomonitors for the availability of other preferred systems and performs“handoffs” to these systems if necessary. “Network selection” is theprocess performed by the mobile station for selecting the communicationnetwork with which to communicate.

Base station transceiver systems may be coupled to different networkswhich may provide different services for a mobile station. ThirdGeneration (3G) wireless networks provide for high speed packet dataservices, a big improvement over earlier developed circuit-switchedwireless networks. As is well documented, 3G services are typicallyassociated with Universal Mobile Telecommunications System (UMTS),Enhanced Data for Global Evolution (EDGE), Wideband Code DivisionMultiple Access (WCDMA), and CDMA2000 (1XRTT, 1XEV-DO, and 1XEV-DV)technologies. On the other hand, Second Generation (2G) communicationservice is a circuit-switched based system and is associated with basicCDMA (e.g. CDMAone), Time Division Multiple Access (TDMA), and GSMtechnologies. 2G typically provides a service that is less than 65kilobits per second (kbps). 2.5 Generation (2.5G) service wasestablished as a bridge to transition from 2G to 3G and is typicallyassociated with CDMA2000 (1×) and General Packet Radio Service (GPRS)technologies. All of the above technologies proceed the primarily“analog” or First Generation (1G) service, which is generally associatedwith Advanced Mobile Phone Service (AMPS).

Using conventional techniques, a mobile station performs networkselection based on information on a Subscriber Identity Module (SIM)card, a Removable User Identity Module (R-UIM), or a Preferred RoamingList (PRL) that resides in non-volatile memory. This information istypically programmed by a service provider and provides the mobilestation with various system selection criteria, such as which systemsthe mobile station should attempt to acquire first, which systems arepreferred over others, which systems are roaming systems, etc. Theselection criteria are usually quite restrictive and do not take intoaccount the primary service that a particular mobile station is expectedto provide.

In contrast to standard cellular telephones, other types of portabledevices such as personal digital assistants (PDAs), laptop computers,and portable e-mail devices, are better known to provide for theorganization and management of text, files, messages, and/or other data.However, wireless data communication services, such as wireless e-mailand Internet access services, are becoming more and more popular inconnection with such devices. Mobile stations providing for combinedcapabilities (e.g. both voice and advanced data communication) alsoexist and are becoming increasingly popular.

In order to operate fully as intended, these mobile stations must havethe appropriate communication services supported and made available bythe communication network that it is registered with. Ideally, acommunication system should support and make available all the differenttypes of communication services that a mobile station is capable ofproviding for the ultimate benefit of the end user. In practice,however, a given communication network can only provide services thatare defined with the standard that it conforms to. For example, a 2 Gcommunication network cannot provide all services defined in 3G.However, there may be other communication networks in the samegeographical area which conform to a more advanced standard and provideservices that are more suitable for the mobile station.

As apparent, conventional network selection does not take intoconsideration the availability of different service offerings in thedecision-making process. As a result, an inadequate communicationnetwork may be selected by the mobile station. For example, a mobilestation may select a communication network that provides an acceptablevoice service (a circuit-switched data service) but not a high speedpacket data service despite the availability of another adequate networkcapable of providing both the voice and the high speed packet dataservice in the same geographical region. Such conventional operation isundesirable, especially for application-specific mobile stations (e.g.portable wireless e-mail devices).

As a particular illustrative example, one conventional network selectioncriteria defined by CDMA service providers involves a preference toselect and communicate with a base station transceiver system of aPersonal Communication Service (PCS) band (i.e. a 1900 MHz band) overthat of a standard cellular network band (i.e. a 800 MHz band). However,the preferred PCS band may or may not offer a 3G service. In fact, thePCS network may provide a 2G service and the standard cellular band mayoffer a 3G service. In such a case, a conventional mobile station willnot provide the data service (e.g. a high speed packet data service) tothe end user even though it is available in the region. Furthermore,there could be other beneficial features in a 3G network, such as a“quick paging channel” in a 1XRTT network. Usage of the quick pagingchannel can significantly increase the standby battery life of themobile station. In certain 2G/3G boundaries, however, if the mobilestation is using conventional network selection methods that do not takeinto account the protocol revision of the transceiver system, the mobilestation may end up in a “more preferred” 2G network and lose the benefitof the quick paging channel. The reverse may also be true in terms ofband preference, since it depends on the band available to the serviceprovider.

Accordingly, there is a resulting need for mobile station methods andapparatus for selecting a communication network that overcome thedeficiencies of the prior art.

SUMMARY

Methods and apparatus for selecting a base station transceiver systembased on service communication type are described. In one illustrativeexample, one or more base station transceiver systems are identified forcommunication with the mobile station through a scanning process. Afirst base station transceiver system is identified as providing a ThirdGeneration (3G) communication service or better, whereas a second basestation transceiver system is identified as failing to provide the 3G orbetter communication service (e.g. it may provide a Second Generation(2G) communication service). The first system is selected forcommunication over the second system based at least in part onidentifying that the second system fails to provide the 3G or bettercommunication service. For example, the first system may be chosen overthe second system if the first system has a signal quality that isbetter than a minimum threshold, even if its signal quality is worsethan that of the second system.

Advantageously, even if a surrounding 2G system has a better signalquality, preference for an adequate 3G or better system is given toensure that a preferred data service is made available to the mobilestation.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of present invention will now be described by way of examplewith reference to attached figures, wherein:

FIG. 1 is a block diagram which illustrates pertinent components of aCode Division Multiple Access (CDMA) wireless communication network anda mobile station which communicates within this network;

FIG. 2 is a more detailed diagram of the mobile station which maycommunicate with one of a plurality of different base stationtransceiver systems which provide services such as a Second Generation(2G) communication service or a Third Generation (3G) or bettercommunication service;

FIG. 3 is a flowchart which describes a method of selecting a basestation transceiver system for communication based on servicecommunication type; and

FIG. 4 is a flowchart which describes an additional method of selectinga base station transceiver system for communication based on servicecommunication type.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the techniques described herein, one or more base station transceiversystems are identified for communication with the mobile station througha scanning process. A first base station transceiver system isidentified as providing a 3 G communication service or better, whereas asecond base station transceiver system is identified as failing toprovide the 3G or better communication service (e.g. it may provide a 2G communication service). The first system is selected for communicationover the second system based at least in part on identifying that thesecond system fails to provide the 3G or better communication service.In another illustrative example of the present techniques, the mobilestation identifies a base station transceiver system that fails toprovide a predetermined digital communication service (e.g. a 3G orbetter service). The mobile station produces and sends a list of one ormore handoff candidate identifiers to a serving base station transceiversystem which excludes an identifier for the system based on its failureto provide the predetermined digital communication service.Advantageously, even if a surrounding 2G system has a better signalquality, preference for an adequate 3G or better system is given toensure that more preferred services of 3G is made available to themobile station.

FIG. 1 is a block diagram of a communication system 100 which includes amobile station 102 which communicates through a wireless communicationnetwork 104. Mobile station 102 preferably includes a visual display112, a keyboard 114, and perhaps one or more auxiliary user interfaces(UI) 116, each of which is coupled to a controller 106. Controller 106is also coupled to radio frequency (RF) transceiver circuitry 108 and anantenna 110.

Typically, controller 106 is embodied as a central processing unit (CPU)which runs operating system software in a memory component (not shown).Controller 106 will normally control overall operation of mobile station102, whereas signal processing operations associated with communicationfunctions are typically performed in RF transceiver circuitry 108.Controller 106 interfaces with device display 112 to display receivedinformation, stored information, user inputs, and the like. Keyboard114, which may be a telephone type keypad or full alphanumeric keyboard,is normally provided for entering data for storage in mobile station102, information for transmission to network 104, a telephone number toplace a telephone call, commands to be executed on mobile station 102,and possibly other or different user inputs.

Mobile station 102 sends communication signals to and receivescommunication signals from network 104 over a wireless link via antenna110. RF transceiver circuitry 108 performs functions similar to those ofa radio network (RN) 128, including for example modulation/demodulationand possibly encoding/decoding and encryption/decryption. It is alsocontemplated that RF transceiver circuitry 108 may perform certainfunctions in addition to those performed by RN 128. It will be apparentto those skilled in art that RF transceiver circuitry 108 will beadapted to particular wireless network or networks in which mobilestation 102 is intended to operate.

Mobile station 102 includes a battery interface 122 for receiving one ormore rechargeable batteries 124. Battery 124 provides electrical powerto electrical circuitry in mobile station 102, and battery interface 122provides for a mechanical and electrical connection for battery 124.Battery interface 122 is coupled to a regulator 126 which regulatespower to the device. When mobile station 102 is fully operational, an RFtransmitter of RF transceiver circuitry 108 is typically keyed or turnedon only when it is sending to network, and is otherwise turned off toconserve resources. Similarly, an RF receiver of RF transceivercircuitry 108 is typically periodically turned off to conserve poweruntil it is needed to receive signals or information (if at all) duringdesignated time periods.

Mobile station 102 operates using a memory module 120, such as aSubscriber Identity Module (SIM) or a Removable User Identity Module(R-UIM), which is connected to or inserted in mobile station 102 at aninterface 118. As an alternative to a SIM or an R-UIM, mobile station102 may operate based on configuration data programmed by a serviceprovider into memory module 120 which is a non-volatile memory. Mobilestation 102 may consist of a single unit, such as a data communicationdevice, a cellular telephone, a multiple-function communication devicewith data and voice communication capabilities, a personal digitalassistant (PDA) enabled for wireless communication, or a computerincorporating an internal modem. Alternatively, mobile station 102 maybe a multiple-module unit comprising a plurality of separate components,including but in no way limited to a computer or other device connectedto a wireless modem. In particular, for example, in the mobile stationblock diagram of FIG. 1, RF transceiver circuitry 108 and antenna 110may be implemented as a radio modem unit that may be inserted into aport on a laptop computer. In this case, the laptop computer wouldinclude display 112, keyboard 114, one or more auxiliary UIs 116, andcontroller 106 embodied as the computer's CPU. It is also contemplatedthat a computer or other equipment not normally capable of wirelesscommunication may be adapted to connect to and effectively assumecontrol of RF transceiver circuitry 108 and antenna 110 of a single-unitdevice such as one of those described above. Such a mobile station 102may have a more particular implementation as described later in relationto mobile station 202 of FIG. 2.

Mobile station 102 communicates in and through wireless communicationnetwork 104. In the embodiment of FIG. 1, wireless network 104 is aThird Generation (3G) supported network based on Code Division MultipleAccess (CDMA) technologies. In particular, wireless network 104 is aCDMA2000 network which includes fixed network components coupled asshown in FIG. 1. Wireless network 104 of the CDMA2000-type includes aRadio Network (RN) 128, a Mobile Switching Center (MSC) 130, a SignalingSystem 7 (SS7) network 140, a Home Location Register/AuthenticationCenter (HLR/AC) 138, a Packet Data Serving Node (PDSN) 132, an IPnetwork 134, and a Remote Authentication Dial-In User Service (RADIUS)server 136. SS7 network 140 is communicatively coupled to a network 142(such as a Public Switched Telephone Network or PSTN), whereas IPnetwork is communicatively coupled to a network 144 (such as theInternet).

During operation, mobile station 102 communicates with RN 128 whichperforms functions such as call-setup, call processing, and mobilitymanagement. RN 128 includes a plurality of base station transceiversystems that provide wireless network coverage for a particular coveragearea commonly referred to as a “cell”. A given base station transceiversystem of RN 128, such as the one shown in FIG. 1, transmitscommunication signals to and receives communication signals from mobilestations within its cell. The base station transceiver system normallyperforms such functions as modulation and possibly encoding and/orencryption of signals to be transmitted to the mobile station inaccordance with particular, usually predetermined, communicationprotocols and parameters, under control of its controller. The basestation transceiver system similarly demodulates and possibly decodesand decrypts, if necessary, any communication signals received frommobile station 102 within its cell. Communication protocols andparameters may vary between different networks. For example, one networkmay employ a different modulation scheme and operate at differentfrequencies than other networks. The underlying services may also differbased on its particular protocol revision.

The wireless link shown in communication system 100 of FIG. 1 representsone or more different channels, typically different radio frequency (RF)channels, and associated protocols used between wireless network 104 andmobile station 102. An RF channel is a limited resource that must beconserved, typically due to limits in overall bandwidth and a limitedbattery power of mobile station 102. Those skilled in art willappreciate that a wireless network in actual practice may includehundreds of cells depending upon desired overall expanse of networkcoverage. All pertinent components may be connected by multiple switchesand routers (not shown), controlled by multiple network controllers.

For all mobile station's 102 registered with a network operator,permanent data (such as mobile station 102 user's profile) as well astemporary data (such as mobile station's 102 current location) arestored in a HLR/AC 138. In case of a voice call to mobile station 102,HLR/AC 138 is queried to determine the current location of mobilestation 102. A Visitor Location Register (VLR) of MSC 130 is responsiblefor a group of location areas and stores the data of those mobilestations that are currently in its area of responsibility. This includesparts of the permanent mobile station data that have been transmittedfrom HLR/AC 138 to the VLR for faster access. However, the VLR of MSC130 may also assign and store local data, such as temporaryidentifications. Mobile station 102 is also authenticated on systemaccess by HLR/AC 138. In order to provide packet data services to mobilestation 102 in a CDMA2000-based network, RN 128 communicates with PDSN132. PDSN 132 provides access to the Internet 144 (or intranets,Wireless Application Protocol (WAP) servers, etc.) through IP network134. PDSN 132 also provides foreign agent (FA) functionality in mobileIP networks as well as packet transport for virtual private networking.PDSN 132 has a range of IP addresses and performs IP address management,session maintenance, and optional caching. RADIUS server 136 isresponsible for performing functions related to authentication,authorization, and accounting (AAA) of packet data services, and may bereferred to as an AAA server.

Those skilled in art will appreciate that wireless network 104 may beconnected to other systems, possibly including other networks, notexplicitly shown in FIG. 1. A network will normally be transmitting atvery least some sort of paging and system information on an ongoingbasis, even if there is no actual packet data exchanged. Although thenetwork consists of many parts, these parts all work together to resultin certain behaviours at the wireless link.

FIG. 2 is a detailed block diagram of a preferred mobile station 202.Mobile station 202 is preferably a two-way communication device havingat least voice and advanced data communication capabilities (i.e.3G-capable), including the capability to communicate with other computersystems. Depending on the functionality provided by mobile station 202,it may be referred to as a data messaging device, a two-way pager, acellular telephone with data messaging capabilities, a wireless Internetappliance, or a data communication device (with or without telephonycapabilities). Mobile station 202 may communicate with any one of aplurality of base station transceiver systems 200 within its geographiccoverage area. Mobile station 202 selects or helps select which one ofbase station transceiver systems 200 it will communicate with (e.g. oneproviding a 3G-service), as will be described in more detail later inrelation to FIGS. 3 and 4.

Mobile station 202 will normally incorporate a communication subsystem211, which includes a receiver 212, a transmitter 214, and associatedcomponents, such as one or more (preferably embedded or internal)antenna elements 216 and 218, local oscillators (LOs) 213, and aprocessing module such as a digital signal processor (DSP) 220.Communication subsystem 211 is analogous to RF transceiver circuitry 108and antenna 110 shown in FIG. 1. As will be apparent to those skilled infield of communications, particular design of communication subsystem211 depends on the communication network in which mobile station 202 isintended to operate.

Mobile station 202 may send and receive communication signals over thenetwork after required network registration or activation procedureshave been completed. Signals received by antenna 216 through the networkare input to receiver 212, which may perform such common receiverfunctions as signal amplification, frequency down conversion, filtering,channel selection, and like, and in example shown in FIG. 2,analog-to-digital (A/D) conversion. A/D conversion of a received signalallows more complex communication functions such as demodulation anddecoding to be performed in DSP 220. In a similar manner, signals to betransmitted are processed, including modulation and encoding, forexample, by DSP 220. These DSP-processed signals are input totransmitter 214 for digital-to-analog (D/A) conversion, frequency upconversion, filtering, amplification and transmission over communicationnetwork via antenna 218. DSP 220 not only processes communicationsignals, but also provides for receiver and transmitter control. Forexample, the gains applied to communication signals in receiver 212 andtransmitter 214 may be adaptively controlled through automatic gaincontrol algorithms implemented in DSP 220.

Network access is associated with a subscriber or user of mobile station202, and therefore mobile station 202 requires a memory module 262, suchas a Subscriber Identity Module or “SIM” card or a Removable UserIdentity Module (R-UIM), to be inserted in or connected to an interface264 of mobile station 202 in order to operate in the network.Alternatively, memory module 262 may be a non-volatile memory which isprogrammed with configuration data by a service provider so that mobilestation 202 may operate in the network. Since mobile station 202 is amobile battery-powered device, it also includes a battery interface 254for receiving one or more rechargeable batteries 256. Such a battery 256provides electrical power to most if not all electrical circuitry inmobile station 202, and battery interface 254 provides for a mechanicaland electrical connection for it. The battery interface 254 is coupledto a regulator (not shown in FIG. 2) which provides power V+ to all ofthe circuitry.

Mobile station 202 includes a microprocessor 238 (which is oneimplementation of controller 106 of FIG. 1) which controls overalloperation of mobile station 202. This control includes network selectiontechniques of the present application. Communication functions,including at least data and voice communications, are performed throughcommunication subsystem 211. Microprocessor 238 also interacts withadditional device subsystems such as a display 222, a flash memory 224,a random access memory (RAM) 226, auxiliary input/output (I/O)subsystems 228, a serial port 230, a keyboard 232, a speaker 234, amicrophone 236, a short-range communications subsystem 240, and anyother device subsystems generally designated at 242. Some of thesubsystems shown in FIG. 2 perform communication-related functions,whereas other subsystems may provide “resident” or on-device functions.Notably, some subsystems, such as keyboard 232 and display 222, forexample, may be used for both communication-related functions, such asentering a text message for transmission over a communication network,and device-resident functions such as a calculator or task list.Operating system software used by microprocessor 238 is preferablystored in a persistent store such as flash memory 224, which mayalternatively be a read-only memory (ROM) or similar storage element(not shown). Those skilled in the art will appreciate that the operatingsystem, specific device applications, or parts thereof, may betemporarily loaded into a volatile store such as RAM 226.

Microprocessor 238, in addition to its operating system functions,preferably enables execution of software applications on mobile station202. A predetermined set of applications which control basic deviceoperations, including at least data and voice communication applications(such as a network re-establishment scheme), will normally be installedon mobile station 202 during its manufacture. A preferred applicationthat may be loaded onto mobile station 202 may be a personal informationmanager (PIM) application having the ability to organize and manage dataitems relating to user such as, but not limited to, e-mail, calendarevents, voice mails, appointments, and task items. Naturally, one ormore memory stores are available on mobile station 202 and SIM 256 tofacilitate storage of PIM data items and other information.

The PIM application preferably has the ability to send and receive dataitems via the wireless network. In a preferred embodiment, PIM dataitems are seamlessly integrated, synchronized, and updated via thewireless network, with the mobile station user's corresponding dataitems stored and/or associated with a host computer system therebycreating a mirrored host computer on mobile station 202 with respect tosuch items. This is especially advantageous where the host computersystem is the mobile station user's office computer system. Additionalapplications may also be loaded onto mobile station 202 through network,an auxiliary I/O subsystem 228, serial port 230, short-rangecommunications subsystem 240, or any other suitable subsystem 242, andinstalled by a user in RAM 226 or preferably a non-volatile store (notshown) for execution by microprocessor 238. Such flexibility inapplication installation increases the functionality of mobile station202 and may provide enhanced on-device functions, communication-relatedfunctions, or both. For example, secure communication applications mayenable electronic commerce functions and other such financialtransactions to be performed using mobile station 202.

In a data communication mode, a received signal such as a text message,an e-mail message, or web page download will be processed bycommunication subsystem 211 and input to microprocessor 238.Microprocessor 238 will preferably further process the signal for outputto display 222 or alternatively to auxiliary I/O device 228. A user ofmobile station 202 may also compose data items, such as e-mail messages,for example, using keyboard 232 in conjunction with display 222 andpossibly auxiliary I/O device 228. Keyboard 232 is preferably a completealphanumeric keyboard and/or telephone-type keypad. These composed itemsmay be transmitted over a communication network through communicationsubsystem 211.

For voice communications, the overall operation of mobile station 202 issubstantially similar, except that the received signals would be outputto speaker 234 and signals for transmission would be generated bymicrophone 236. Alternative voice or audio I/O subsystems, such as avoice message recording subsystem, may also be implemented on mobilestation 202. Although voice or audio signal output is preferablyaccomplished primarily through speaker 234, display 222 may also be usedto provide an indication of the identity of a calling party, duration ofa voice call, or other voice call related information, as some examples.

Serial port 230 in FIG. 2 is normally implemented in a personal digitalassistant (PDA)-type communication device for which synchronization witha user's desktop computer is a desirable, albeit optional, component.Serial port 230 enables a user to set preferences through an externaldevice or software application and extends the capabilities of mobilestation 202 by providing for information or software downloads to mobilestation 202 other than through a wireless communication network. Thealternate download path may, for example, be used to load an encryptionkey onto mobile station 202 through a direct and thus reliable andtrusted connection to thereby provide secure device communication.

Short-range communications subsystem 240 of FIG. 2 is an additionaloptional component which provides for communication between mobilestation 202 and different systems or devices, which need not necessarilybe similar devices. For example, subsystem 240 may include an infrareddevice and associated circuits and components, or a Bluetooth™communication module to provide for communication with similarly-enabledsystems and devices. Bluetooth™ is a registered trademark of BluetoothSIG, Inc.

FIG. 3 is a flowchart which describes a mobile station method ofselecting a base station transceiver system with a preference for 3Gservices (e.g. packet data services) over 2G services during an idlemode of the mobile station. Although the method of FIG. 3 will bedescribed with respect to a single candidate system under considerationfor illustrative clarity, it may be employed for a plurality ofcandidate systems under simultaneous consideration. Prior to the stepsdescribed in relation to FIG. 3, the mobile station scans a geographiccoverage area to identify one or more available candidate base stationtransceiver systems with which it may communicate. In CDMA, each RadioNetwork (RN) includes multiple base station transceiver systems whichare identified by the phase of a Pseudorandom Noise (PN) code. Thus, themobile station scans for PNs on a number of different frequencies asdirected by its Preferred Roaming List (PRL) in its R-UIM ornon-volatile memory.

From a start block 302, the mobile station acquires a system inaccordance with its PRL and roaming settings (step 304). The mobilestation may alternatively acquire a system in step 304 that is not inthe PRL by means of idle handoff and channel hashing, for example. Thisinitially acquired system may be, for example, a 2G system or a 3Gsystem, and may not even be a preferred system. After systemacquisition, the mobile station begins to periodically scan for systemsthat may be more suitable for its primary service (e.g. packet dataservice) or new geographic location. This periodic scanning could be theresult of a periodic reselection process when the mobile station is in aless preferred system per its PRL, or merely the result of a neighborsystem search during every wake-up period from sleep mode (a list of theneighboring base stations is provided by the current base stationtransceiver system).

During its scanning, the mobile station maintains a table of systeminformation for candidate and neighboring base station transceiversystems. This table is created based on operational observations anddata actually received from most if not all systems including previouslyacquired systems. The mobile station also measures various metrics ofsignal quality of the current system as well as its candidate andneighboring systems in the table. In CDMA, the signal strength istypically determined based on a plurality of measured parameters, suchas the total received power of the spectrum, chip energy of the pilotchannel over total noise (E_(c)/I_(o)), etc. Typically, the pilotchannel E_(c)/I_(o) is used as the measure of signal quality of thesystem.

In accordance with the present application, and as will be described indetail, the criteria for considering a candidate system to be “better”than the current system for handoff purposes depends on whether thetransition is from 2G to 3G or vice versa, the relative signal strengthsof the systems, knowledge of the actual data service access in the 3Gsystem, and so on. Thus, after the initial system is acquired at step304, the mobile station identifies whether a candidate system is onethat is associated with a Second Generation (2G) communication serviceor a Third Generation (3G) communication service (step 306). If thecandidate system is associated with the 2G service, the flowchartfollows the “2G” branch from step 306. If the candidate system isassociated with the 3G service, the flowchart follows the “3G” branchfrom step 306.

If the candidate system is associated with the 2G service at step 306,then the “2G” branch from step 306 is followed where the mobile stationidentifies whether the current system is one that is associated with 2Gor 3G (step 308). If the current system is associated with 2G, then the“2G” branch from step 308 is followed where the mobile station willconsider conventional handoff techniques (step 338 through a connectorA1). When conventional handoff techniques are considered at step 338,the mobile station facilitates a handoff to the candidate system if itssignal quality is stronger than the signal quality of the currentsystem. Conversely, if the signal quality of the candidate system is notbetter than that of the current system, then a handoff to the candidatesystem is not initiated and communication is maintained with the currentsystem. In the present embodiment, the signal quality of the candidatesystem is better or greater than that of the current system if thecandidate's system is at least 2 dB greater than that of the currentsystem.

If the current system is associated with 3G as identified in step 308,however, the “3G” branch from step 308 is followed. Here, the mobilestation identifies whether the current system actually grants 3G service(step 312). If the current system does not actually grant 3G service,then the mobile station considers conventional handoff techniques asdescribed above (step 338 through connector A1). If the current systemdoes indeed grant 3G service as tested at step 312, however, the mobilestation facilitates a handoff to the candidate 2G system only if thesignal quality of the current 3G system is less than a minimum threshold(“MIN_THRESH”) and the signal quality of the candidate 2G system isgreater than that of the current 3G system (step 314). Conversely instep 314, if the signal quality of the current 3G system is greater thanor equal to the minimum threshold, or the signal quality of thecandidate 2G system is less than the current 3G system, a handoff to thecandidate 2G system is not initiated and communication is maintainedwith the current 3G system. Based on the above, the mobile station willmaintain communication with the current 3G system even if its signalstrength is worse than the signal strength of the candidate 2G system,as long as the current 3G system is greater than or equal to the minimumthreshold.

Preferably, the minimum threshold represents a relatively low butnonetheless acceptable and suitable signal quality for communication ina system that provides the desired services to the mobile station. Forexample, the minimum threshold can be set to −12 dB if E_(c)/I_(o) isused as the measure of signal quality. Any suitable signal threshold maybe utilized, however, preferably within the range of between −10 and −14dB.

In step 306, if the candidate system is associated with the 3G servicethen the “3G” branch from step 306 is followed. In this case, the mobilestation identifies whether the current system is associated with 2G or3G (step 322). If the current system is associated with 2G as identifiedat step 322, then the “2G” branch from step 322 is followed to step 330through a connector A2. At step 330, the mobile station facilitates ahandoff to the candidate 3G system if its signal quality is greater thanor equal to a minimum threshold (“MIN_THRESH” in step 330). Conversely,if the signal quality of the candidate 3G system is less than theminimum threshold, a handoff to the candidate 3G system is not initiatedand communication is maintained with the current system. In the presentembodiment, the minimum threshold is −14 dB (i.e. the same threshold asthat used in step 314). Based on the above, the mobile station willhandoff to the candidate 3G system even if its signal quality is worsethan that of the current system, as long as the candidate 3G system isgreater than or equal to the minimum threshold.

In step 322, if the current system is associated with the 3G servicethen the “3G” branch from step 322 is followed. Here, the mobile stationidentifies whether the current system actually grants 3G service or not(step 326). If the current system does not grant 3G service asidentified in step 326, then the mobile station identifies whether thecandidate system was previously granted 3G service in an earlier visit(step 328). If not, then the mobile station considers conventionalhandoff techniques as described above (step 338 through connector A1).If the candidate system was previously granted 3G service as identifiedin step 328, then the mobile station facilitates a handoff to thecandidate 3G system if its signal quality is greater than or equal to aminimum threshold (step 330). Conversely in step 330, if the signalquality of the candidate 3G system is less than the minimum threshold, ahandoff to the candidate 3G system is not initiated and communication ismaintained with the current system. In the present embodiment, theminimum threshold is −14 dB (i.e. the same threshold as that used instep 314). Based on the above, the mobile station will again handoff tothe candidate 3G system even if its signal quality is worse than that ofthe current system, as long as the candidate 3G system is greater thanor equal to the minimum threshold.

In step 326, if the current system grants 3G service then the mobilestation identifies whether the candidate system was previously granted3G service in an earlier visit (step 332). If so, then the mobilestation considers conventional handoff techniques as described above(step 338 through connector A1). If the candidate system was neverpreviously granted 3G service as identified in step 332, then the mobilestation facilitates a handoff to the candidate 3G system if the signalquality of the current 3G system is less than the minimum threshold andthe signal quality of the candidate system is stronger than the current3G system (step 334). Conversely in step 334, if the signal quality ofthe current 3G system is greater than or equal to the minimum threshold,or the signal quality of the candidate 3G system is less than thecurrent 3G system, a handoff to the candidate 3G system is not initiatedand communication is maintained with the current 3G system.

In step 306, if the candidate system is not listed in the table ofsystems that the mobile station maintains, it is unknown whether thecandidate system is associated with a 2G or 3G service. In this case,the “unknown” branch from step 306 is followed. The candidate system'sservice status (i.e. 2G or 3G) is identified and the table of systeminformation is updated with this and other appropriate informationregarding the base station transceiver system (step 318). The mobilestation considers conventional handoff techniques regarding the currentand candidate systems (step 338 through a connector A1).

Thus, according to the method of FIG. 4, one or more base stationtransceiver systems are identified for communication with the mobilestation through a scanning process. A first base station transceiversystem is identified as providing a 3G or better communication service,whereas a second base station transceiver system is identified asfailing to provide the 3G or better communication service (e.g. it mayprovide a 2 G communication service). The first system is selected forcommunication over the second system based at least in part onidentifying that the second system fails to provide the 3G or bettercommunication service. Advantageously, even if a surrounding 2G systemhas a better signal quality, preference for an adequate 3G or bettersystem is given to ensure that a preferred 3G service (e.g. high speedpacket data service or quick paging) is made available to the mobilestation.

FIG. 4 is a flowchart which describes a method of selecting a basestation transceiver system for communication with the mobile stationduring an access or traffic state of the mobile station. The methoddescribed in relation to FIG. 4 relates to the creation of anidentifying list of candidate base station transceiver systems availablefor handoff and communication with the mobile station. This handoffcandidate list of base station transceiver system identifiers istransmitted in a message by the mobile station to a serving base stationtransceiver system. The list may be transmitted in a message such as anOrigination Message, a Page Response Message during a call setup (i.e.access state), and a Pilot Strength Measurement Message (PSMM) during ahandoff request (i.e. traffic state), as examples. After transmission,the mobile station will be handed-off to and communicate with a basestation transceiver system that is ultimately selected by the network.

Prior to the steps described in relation to FIG. 4, the mobile stationscans a geographic coverage area to identify one or more availablecandidate base station transceiver systems (or available candidate“PNs”) with which it may communicate. Beginning at a start block 402,the mobile station identifies a candidate system to consider forinclusion into the handoff candidate list of base station transceiversystem identifiers (step 404). The mobile station identifies whether asignal quality of the candidate system is greater than or equal to aminimum handoff threshold (“MIN_HANDOFF_THRESH”) (step 406). If thecandidate system is less than the minimum handoff threshold, anidentifier for the candidate system is not included in the list (“NO”branch from step 406). The mobile station identifies whether there areadditional candidate systems to consider (step 416); if so, theflowchart continues again at step 404.

If the signal quality of the candidate system is greater than or equalto the minimum handoff threshold in step 406, however, the mobilestation will proceed to consider including it into the list. Inparticular, the mobile station identifies whether the candidate systemis associated with a Second Generation (2G) communication service or aThird Generation (3G) communication service (step 408). If the candidatesystem is associated with the 2G service, the flowchart follows the “2G”branch from step 408. If the candidate system is associated with the 3Gservice, the flowchart follows the “3G” branch from step 408.

If the candidate system is associated with the 2G service (“2G” branchfrom step 408), the mobile station identifies whether it is currentlyoperating with a 2G service or a 3G service (step 410). If the mobilestation is currently operating with a 2G service (“2G” branch from step510), the candidate system is added to the list of handoff candidates(step 414). If the mobile station is currently operating with a 3Gservice (“3G” branch from step 410), however, the candidate system isnot included in the list. The mobile station identifies whether thereare additional candidate systems to consider (step 416); if so, theflowchart continues again at step 404.

If the candidate system is associated with the 3G service (“3G” branchfrom step 408), the mobile station identifies whether data service waspreviously declined for the candidate system (step 412). If thecandidate system did not previously decline the data service (“NO”branch from step 412), the candidate system is added to the list ofhandoff candidates (step 414). If the candidate system previouslydeclined the data service (“YES” branch from step 412), however, thecandidate system is not included in the list. The mobile stationidentifies whether there are additional candidate systems to consider(step 416); if so, the flowchart continues again at step 404.

If there are no other candidate systems to consider from step 416, themobile station transmits a message that includes the list to the servingbase station transceiver system (step 418). Subsequently, the networkdecides which base station transceiver system is most suitable forcommunication with the mobile station based on the identifiers in thelist. The mobile station is then handed-off to and communicates with theselected base station transceiver system. As described above, the listmay be transmitted in messages such as an Origination Message, a PageResponse Message, and a Pilot Strength Measurement Message (PSMM), asexamples.

Thus, according to the method of FIG. 4, one or more base stationtransceiver systems are identified for communication with a mobilestation through a scanning process. The mobile station identifies a basestation transceiver system that fails to provide a predetermined digitalcommunication service. The mobile station produces and sends a list ofone or more handoff candidate identifiers to a serving base stationtransceiver system which excludes an identifier for the base stationtransceiver system based on its failure to provide the predetermineddigital communication service. Preferably, the predetermined digitalcommunication service is a 3G or better communication service.Advantageously, even if a surrounding 2G base station transceiver systemhas a better signal quality, preference for an adequate 3G or betterbase station transceiver system is given to ensure that a preferred 3Gservice is made available to the mobile station.

Description will now be provided regarding how the mobile stationidentifies the type of communication service (e.g. 2G or 3G) that isprovided for each base station transceiver system, and whether any 3Gdata service was actually previously denied for that base stationtransceiver system. In the methods described in relation to FIGS. 3 and4, the mobile station stores and maintains a list of information in itsmemory corresponding to each base station transceiver system. Arepresentative example of some of pertinent information regarding eachbase station transceiver system is represented in Table 1 below.

TABLE 1 List of base station system information stored in the mobilestation, which includes an indication of the service type (e.g. 2G or3G) associated with each system identifier. Base station System ServicePrevious transceiver Identification Frequency PN Type (e.g. 3G Servicesystem (SID) Number Code 2G or 3G) Denial ? 1 SID₁ f₁ PN₁ 2G N/A 2 SID₂f₂ PN₂ 3G NO 3 SID₃ f₃ PN₃ 3G YES 4 SID₄ f₄ PN₄ 2G N/A 5 SID₄ f₄ PN₅ 2GN/A 6 SID₄ f₅ PN₄ 3G YES . . . . . . . . . . . . . . . . . . N SID_(N)f_(N) PN_(N) 3G NO

As shown in Table 1 above, information is stored and maintained for aplurality of N base station transceiver systems. In this embodiment, thebase station transceiver systems represent the last twenty (20) basestation transceiver systems encountered by the mobile station. That is,the list is continually updated by the mobile station over time to storeinformation associated with the previous ten base station transceiversystems encountered. Although in this embodiment N=20, N may be anysuitable number. As indicated in the table, the information associatedwith each base station transceiver system identifier includes aparticular System Identification (SID), frequency number, andpseudorandom noise (PN) sequence code.

In addition, the stored list also associates a particular communicationservice type (e.g. 2G or 3G) for each base station transceiver system.When the mobile station encounters a new base station transceiver systemthat is not included in the list, the system is of an “unknown”communication service type. In that case, the mobile station maysubsequently determine what communication service type is provided andupdate the table with the communication service type and otherinformation.

The mobile station may identify or determine the communication servicetype (e.g. 2G or 3G) using any suitable technique. In the presentembodiment, the mobile station determines what communication servicetype is available based on parameters transmitted from the base stationtransceiver system. In particular, some parameters broadcasted on apaging channel are indicative of the service communication type. InCDMA2000, for example, if the protocol revision (P_REV) broadcasted onthe paging channel is greater than or equal to six (6), then the mobilestation can assume that the base station transceiver system supportspartial or full 3G services. Transmission of an “extended channel listmessage” by the base station transceiver system also serves as anindication that serving base station transceiver system supports partialor full 3G services. Again, however, any suitable technique to identifythe communication service type may be utilized.

Final Comments.

In the techniques described herein, one or more base station transceiversystems are identified for communication with the mobile station througha scanning process. A first base station transceiver system isidentified as providing a 3 G communication service or better, whereas asecond base station transceiver system is identified as failing toprovide the 3G or better communication service (e.g. it may provide a 2G communication service). The first system is selected for communicationover the second system based at least in part on identifying that thesecond system fails to provide the 3G or better communication service.Advantageously, even if a surrounding 2G system has a better signalquality, preference for an adequate 3G or better system is given toensure that a preferred data service (e.g. high speed packet dataservice or quick paging channel) is made available to the mobilestation.

In another illustrative example of the present techniques, one or morebase station transceiver systems are identified for communication with amobile station through a scanning process. The mobile station identifiesa base station transceiver system that fails to provide a predetermineddigital communication service. The mobile station produces and sends alist of one or more handoff candidate identifiers to a serving basestation transceiver system which excludes an identifier for the systembased on its failure to provide the predetermined digital communicationservice. Preferably, the predetermined digital communication service isa 3G or better service. Advantageously, even if a surrounding 2G systemhas a better signal quality, preference for an adequate 3G or bettersystem is given to ensure that a preferred data service (e.g. a packetdata service) is made available to the mobile station.

The above-described embodiments of the present application are intendedto be examples only. Those of skill in the art may effect alterations,modifications and variations to the particular embodiments withoutdeparting from the scope of the application. For example, although theabove description refers to 3G as the preferred communication service,over time even better technologies will be implemented and referred tounder a different name (e.g. 3.5G, 4G, etc.) and the invention embracessuch technologies. Furthermore, some mobile stations may be operable toprovide the same or similar preference or bias towards a 2G system overa 3G system. For example, a voice-only mobile station may prefer 2G over3G since 2G service operation may provide a lower power consumption than3G service operation. The invention described herein in the recitedclaims intends to cover and embrace all such changes in technology.

The invention claimed is:
 1. In a mobile station connected to a firstcellular base station transceiver system, a method of selecting acellular base station transceiver system for communication with themobile station, the method comprising; scanning to identify a secondcellular base station transceiver system for communication; identifying,at the mobile station, that the second cellular base station transceiversystem provides a predetermined communication service, and that thefirst cellular base station transceiver system fails to provide thepredetermined communication service but provides a service that is lesspreferred than the predetermined communication service; and in responseto the identifying, causing the second cellular base station transceiversystem to be selected for communication over the first cellular basestation transceiver system even if signal quality of the second cellularbase station transceiver system is worse than that of the first cellularbase station transceiver system; wherein identifying whether at leastone of the first cellular base station transceiver system fails toprovide the predetermined communication service and the second cellularbase station transceiver systems provides the predeterminedcommunication service is based on identifying one or more parameterstransmitted by at least one of the first and second cellular basestation transceiver systems.
 2. The method of claim 1, wherein thepredetermined communication service comprises a Third Generation (3G)communication service.
 3. The method of claim 1, wherein the act ofidentifying whether the first and second cellular base stationtransceiver systems provide a predetermined communication servicefurther comprises identifying whether an extended channel list messageis transmitted from the first and the second cellular base stationtransceiver systems.
 4. The method of claim 1, wherein causing thesecond cellular base station transceiver system to be selected forcommunication over the first cellular base station transceiver systemfurther comprises producing and sending a list of handoff candidateidentifiers which includes a second identifier for the second cellularbase station transceiver system but excludes a first identifier for thefirst cellular base station transceiver system.
 5. The method of claim1, wherein the signal quality is based on an energy-to-interferenceratio (E_(C)/I_(O)), the method further comprising: measuring, from thescanning, a first E_(C)/I_(O) of the first cellular base stationtransceiver system; and measuring, from the scanning, a secondE_(C)/I_(O) of the second cellular base station transceiver system. 6.The method of claim 1, wherein the predetermined communication servicecomprises a Fourth Generation (4G) communication service.
 7. A mobilestation comprising: a controller; a radio frequency (RF) transceivercoupled to the controller; the controller being configured to: scan,with use of the RE transceiver, to identify a second cellular basestation transceiver system for communication; identify that the secondcellular base station transceiver system provides a predeterminedcommunication service, and that the first cellular base stationtransceiver system fails to provide the predetermined communicationservice; and in response to the identifying, cause the second cellularbase station transceiver system to be selected for communication overthe first cellular base station transceiver system even if a signalquality of the second cellular base station transceiver system is worsethan that of the first cellular base station transceiver system butprovides a service that is less preferred than the predeterminedcommunication service; wherein identifying whether at least one of thefirst cellular base station transceiver system fails to provide apredetermined communication service and the second cellular base stationtransceiver systems provides the predetermined communication service isbased on identifying a protocol version broadcasted on a paging channelof parameter transmitted by at least one of the first and secondcellular base station transceiver systems.
 8. The mobile station ofclaim 7, wherein the predetermined communication service comprises aThird Generation (3G) communication service.
 9. The mobile station ofclaim 7, wherein the controller is further configured to identifywhether the first and second cellular base station transceiver systemsprovide a predetermined communication service by identifying whether anextended channel list message is transmitted from the first and thesecond cellular base station transceiver systems.
 10. The mobile stationof claim 7, wherein the controller is configured to cause the secondcellular base station transceiver system to be selected forcommunication over the first cellular base station transceiver system byproducing and sending a list of handoff candidate identifiers whichincludes a second identifier for the second cellular base stationtransceiver system but excludes a first identifier for the firstcellular base station transceiver system.
 11. A communication system,comprising: a first cellular base station transceiver system; a secondcellular base station transceiver system; one or more mobile stationsoperative for communications via the first and the second cellular basestation transceiver system; each mobile station being configured to:scan to identify a second cellular base station transceiver system forcommunication; identify that the second cellular base stationtransceiver system provides a predetermined communication service, andthat the first cellular base station transceiver system fails to providethe predetermined communication service but provides a service that isless preferred than the predetermined communication service; and inresponse to the identifying, cause the second cellular base stationtransceiver system to be selected for communication over the firstcellular base station transceiver system even if a signal quality of thesecond cellular base station transceiver system is worse than that ofthe first cellular base station transceiver system; wherein identifyingwhether at least one of the first cellular base station transceiversystem fails to provide a predetermined communication service and thesecond cellular base station transceiver systems provides thepredetermined communication service is based on identifying a protocolversion broadcasted on a paging channel of parameter transmitted by atleast one of the first and second cellular base station transceiversystems.
 12. The communication system of claim 11, wherein thepredetermined communication service comprises a Third Generation (3G)communication service.
 13. The method of claim 1, wherein thepredetermined communication service comprises a voice communicationservice.
 14. The method of claim 1, wherein the predeterminedcommunication service comprises a GERAN communication service.
 15. Themobile station of claim 7, wherein the predetermined communicationservice comprises a voice communication service.
 16. The mobile stationof claim 7, wherein the predetermined communication service comprises aGERAN communication service.
 17. The communication system of claim 11,wherein the predetermined communication service comprises a voicecommunication service.
 18. The communication system of claim 11, whereinthe predetermined communication service comprises a GERAN communicationservice.